1. Field of the Invention
The present invention concerns a dispensing head and unit provided with a closing system permitting fresh air intake.
2. Description of the Related Art
FIG. 1 discloses a conventional dispensing head mounted on a manually deformable container, as in FR-A-2705650, which is hereby incorporated by reference. Apart from the rigid element (11) defining the dispensing duct (16), this dispensing head comprises an elastic part or obturator (12) which rests on a seat (15) of the rigid element (11) and is retained by a flange (19). An opening (14) separates the obturator (12) from a raised edge (18) of the seat. The elastic part (12) is obtained by partly overmolding in situ a bar-shaped attachment element (13) made of a rigid material forming part of the rigid element (11), in a second stage after the initial molding operation of the rigid element (11).
However, since the obturator (12) returns into a position of completely leakproof contact with the seat (15) when the dispensing has been stopped, such a dispensing head does not permit fresh air return flow for pressure equalization, and so the container deforms because of the low pressure inside the container. Apart from reduced aesthetic qualities, this deformation results in a less satisfactory ease of manipulation of the container. Moreover, the rate of emptying of a container without pressure equalization is lower than that of a container permitting pressure equalization.
FIGS. 2 and 3 schematically show the molding of the one-piece dispensing head described above by the additional injection moulding of a flexible elastic material S around the rigid attachment element (23) forming part of the element (21). In a first stage, the two mold halves M1 and M2 of the molding machine, each comprising a mold slide T1 or T2 are closed and the rigid material R, for example polypropylene at a temperature of approximately 160.degree. C., is injected into the mold to produce the rigid element (21). In a second stage, as shown in FIG. 3, the valve slides T1 and T2 are moved away in the direction of arrows F1, F2 by a distance which corresponds approximately to the thickness of the obturator (32). Then, at a temperature of preferably less than 160.degree. C., the elastic material such as ethylene vinyl acetate is injected so as to surround the attachment bar (23). Thus the obturator (32) is solidly anchored in the dispensing duct without any chemical bond being created between the obturator (32) and its seat (35). This molding operation, which is very simple, makes it possible to manufacture the dispensing head in a single molding cycle without using elastomeric obturators which require an additional, curing step.
EP-A-452196 and U.S. Pat. No. 4,314,658 disclose dispensing heads provided with obturators opening by elastic deformation and permitting venting or fresh air intake. However, these dispensing heads are constituted by several assembled mechanical components. The molding of a mechanical component is an expensive operation and it is desirable to reduce the number of these components to reduce the cost of the unit.